Support pluralization in I18n messages backend

Pass all provided options down to I18n.t method. It will use `:count`
option to pluralize the message.

  en:
    foo:
      one: %{count} foo
      other: %{count} foos

  I18n.t(:foo, count: 1) #=> 1 foo
  I18n.t(:foo, count: 1) #=> 2 foos

lib/dry/schema/messages/i18n.rb

@@ -32,7 +32,8 @@ def initialize
         def get(key, options = EMPTY_HASH)
           return unless key
 
-          result = t.(key, locale: options.fetch(:locale, default_locale))
+          options = { locale: default_locale, **options }
+          result = t.(key, **options)
 
           if result.is_a?(Hash)
             text = result[:text]

spec/integration/messages/i18n_spec.rb

@@ -203,6 +203,42 @@ def store_errors(**errors)
           expect(meta).to eql(code: 123)
         end
       end
+
+      context "with plural message" do
+        before do
+          store_errors(
+            apples: {
+              one: "single apple",
+              other: "%{count} apples"
+            }
+          )
+        end
+
+        it "uses correct variant" do
+          template, meta = messages[:apples, path: :path, count: 3]
+
+          expect(template.()).to eql("3 apples")
+          expect(meta).to eql({})
+        end
+
+        context "without count" do
+          it "returns meta" do
+            template, meta = messages[:apples, path: :path]
+
+            expect(template.()).to eql({
+              one: "single apple",
+              other: "%{count} apples"
+            })
+
+            expect(template.(count: 1)).to eql("single apple")
+
+            expect(meta).to eql({
+              one: "single apple",
+              other: "%{count} apples"
+            })
+          end
+        end
+      end
     end
 
     context "with dynamic locale" do